ath79: add support for Compex WPJ531 (16M)

Specifications:

SoC: QCA9531
DRAM: 128MB DDR2
Flash: 16MB SPI-NOR
2 100MBit ethernet ports
2×2 2.4GHz on-board radio
miniPCIe slot that supports 5GHz radio
PoE 24V - 48V IEEE 802.3af optional
USB 2.0 header

Installation:

To install, start a tftp server in bin/targets/ath79/generic/ and use the
u-boot prompt over UART:

tftpboot 0x80500000 openwrt-ath79-generic-compex_wpj531-16m-squashfs-sysupgrade.bin
erase 0x9f030000 +$filesize
erase 0x9f680000 +1
cp.b $fileaddr 0x9f030000 $filesize
boot

The cpximg file can be used with sysupgrade in the stock firmware (add SSH key
in luci for root access).

Another way is to hold the reset button during power up or running 'cpximg' in
the u-boot prompt.
Once the last LED starts flashing regularly, a TFTP-server under 192.168.1.1
will accept the image appropriate for the board revision that is etched on the
board.

For example, if the board is labelled '7A04':

tftp -v -m binary 192.168.1.1 -c put openwrt-ath79-generic-compex_wpj531-16m-squashfs-cpximg-7A04.bin

MAC addresses:

<&uboot 0x2e010>  *:cb  (label)
<&uboot 0x2e018>  *:cc
<&uboot 0x2e020>  *:cd
<&uboot 0x2e028>  *:ce

Only the first two are used (for ethernet), the WiFi modules have
separate (valid) addresses. The latter two addresses are not used.

Signed-off-by: Leon M. George <leon@georgemail.eu>
[commit title/message facelift, fix rssileds, add led aliases]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath79/image/generic.mk

@@ -418,6 +418,17 @@ define Device/comfast_cf-wr752ac-v1
 endef
 TARGET_DEVICES += comfast_cf-wr752ac-v1
 
+define Device/compex_wpj531-16m
+  SOC := qca9531
+  DEVICE_PACKAGES := kmod-usb2
+  IMAGE_SIZE := 16128k
+  DEVICE_VENDOR := Compex
+  DEVICE_MODEL := WPJ531
+  DEVICE_VARIANT := 16M
+  SUPPORTED_DEVICES += wpj531
+endef
+TARGET_DEVICES += compex_wpj531-16m
+
 define Device/devolo_dvl1200e
   SOC := qca9558
   DEVICE_VENDOR := devolo